I have irregular period and my boyfriends cums inside of me all the time, im having brown discharge and mild cramping could i be expecting?

Yes: It is a significant possibility given your pattern described. If not pregnant now, your frequent exposure to sperm and irregularity of menstrual cycling is a formula for pregnancy in the future. If not desired, would see doctor and discuss options to prevent pregnancy until desired.

Pregnancy: Yes, especially if you are not using precautions and anticontraceptives, do the pregnancy test, if negative, then see your obgyn.